New Hampshire is getting a $3.6 million federal grant to build on drug- and alcohol-abuse prevention efforts among young people. Joe Harding, director of the state Health Department’s Bureau of Drug and Alcohol Services Administration, said Monday that the three-year grant will help direct prevention efforts to ‘‘those at greatest risk in areas of our state with the greatest need.’’ The efforts are focused on reducing underage drinking among people age 12 to 20 and preventing prescription drug misuse and abuse among people age 12 to 25.